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Re: qemu m68k/mcf5208: problem with signal handler

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Hi Waldemar,

On 09/05/16 18:58, Waldemar Brodkorb wrote:
> Hi,
>
> forgot to add Greg in CC.
> And sorry for the whitespace fuckup in the example code.
>
> Waldemar Brodkorb wrote,
>
>> Dear kernel hackers,
>>
>> I have a problem with the signal handling under qemu-system-m68k
>> emulating coldfire mcf5208 evalboard. Following example code
>> provided by Busybox maintainer Denys Vlasenko
>> shows the problem when running on qemu:
>
> [ .. ]
>
>> You can generate a bootable image with latest buildroot, which shows the issue:
>> $ git clone git://git.buildroot.net/buildroot
>> $ cd buildroot; make qemu_m68k_mcf5208_defconfig; make
>> $ qemu-system-m68k -M mcf5208evb -cpu m5208 -kernel output/images/vmlinux -nographic
>>
>> Every command forked from busybox hush shell will lead into a segmentation fault.
>>
>> I added following printk to start investigating the problem:
>> diff -Nur linux-4.5.3.orig/arch/m68k/kernel/signal.c linux-4.5.3/arch/m68k/kernel/signal.c
>> --- linux-4.5.3.orig/arch/m68k/kernel/signal.c	2016-05-04 23:50:38.000000000 +0200
>> +++ linux-4.5.3/arch/m68k/kernel/signal.c	2016-05-09 04:24:53.885199544 +0200
>> @@ -595,6 +595,7 @@
>>   			       void __user *fp)
>>   {
>>   	int fsize = frame_extra_sizes(formatvec >> 12);
>> +	printk("avoid broken signal handler...\n");
>>   	if (fsize < 0) {
>>   		/*
>>   		 * user process trying to return with weird frame format
>>
>> But now the problem disappeared. :/
>>
>> What do you think? Is it a Kernel bug or a C library problem?

What version of linux kernel?
What version of gcc?

This sounds a lot like the problem I fixed in linux commit a9551799
("m68k: Use conventional function parameters for do_sigreturn").

Definitely try that first.

Regards
Greg


>> Busybox hush otherwise works fine for other noMMU targets as stm32
>> evalboard with cortex-m4. It also works in Qemu M68k emulating Q800
>> full MMU system.
>>
>> Thanks for any ideas,
>>   Waldemar
>>
>> http://lists.busybox.net/pipermail/busybox/2014-September/081659.html
>>
>

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qemu m68k/mcf5208: problem with signal handler Waldemar Brodkorb <wbx@openadk.org> - 2016-05-09 08:50 +0200
  Re: qemu m68k/mcf5208: problem with signal handler Waldemar Brodkorb <wbx@openadk.org> - 2016-05-09 11:00 +0200
    Re: qemu m68k/mcf5208: problem with signal handler Greg Ungerer <gerg@uclinux.org> - 2016-05-09 16:00 +0200
      Re: qemu m68k/mcf5208: problem with signal handler Waldemar Brodkorb <wbx@openadk.org> - 2016-05-09 18:30 +0200

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